Anti-friction bearing and a motor such a bearing

ABSTRACT

An anti-frictional bearing which is reduced in its asynchronous rotational run out so that the cumbersome analyzing operation of the raceway surface and selecting operation of inner and/or outer races are not required. The bearing will contribute for the high packaging density and high speed operation of the hard disk device.  
     An anti-frictional bearing including an inner race way  1   a  formed on an outer peripheral surface of an inner race  1,  an outer race way  2   a  formed on an inner peripheral surface of an outer race  2,  and a plurality of rotating bodies  3  interposed between the race ways and retained by retainers  4  in a predetermined distance with each other, wherein an out of roundness of a raceway surface  1   a,    2   a  of at least one of said inner and outer races  1, 2  is equal to or less than 0.05 μm.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field

[0002] The present invention relates to an anti-frictional bearingconstituting a rotationally supporting portion of a spindle motor of ahard disk drive device, VTR, and so on. The present invention furtherrelates to a motor into which such a bearing is incorporated.

[0003] 2. Description of the Prior Art

[0004] The compact hard disk device to be incorporated into a personalcomputer includes magnetic disk or disks driven by means of spindlemotor in high rotational speed. The rotational member of such motor isadapted to be journalled through an anti-friction bearing having aninner diameter of 4-6 mm and an outer diameter of 8-15 mm.

[0005] Recently, a remarkable development or improvement is achieved inthe hard disk device regarding the miniaturization and high packagingdensity. Especially for the hard disk device the size of which is equalto or less than 3.5 inch, the packaging density is increased rapidly.More recently, the hard disk device of the size of 2.5 inch to beincorporated into the hand held personal computer of the note book typeis also demanded to have substantially the same memory capacity as thatof the hard disk device of 3.5 inch in spite of its small size.

[0006] In order to enlarge the memory capacity of the hard disk deviceof the size of 2.5 inch, it is necessary to increase both of the trackrecording density and the track density. The presently demanded trackdensity from 10 KTPI to 14 KTPI (TPI: Track Per Inch) can be satisfiedby the track pitch less than 2.54 μm. This value of the track pitchcorresponds with the track density of 10 KTPI.

[0007] In either hard disk device the size of which is 3 5 inch or 2.5inch, it is necessary to increase the number of revolution of themagnetic disk or disks to increase the data transfer rate of the harddisk device. For example, the hard disk device of 3.5 inch requires thenumber of revolution from 5400 rpm to 7200 rpm, and the hard disk deviceof 2.5 inch requires the number of revolution from 4000 rpm to 5000 rpm.

[0008] When it is intended to read or write datum accurately into themagnetic disk of increased track density, it is necessary to reduce therotational run out of the magnetic disk. The rotational run out is aptto increase in proportion to the number of revolution of the magneticdisk. It is therefore important in the high packaging density of thehard disk device to improve the precision of the rotational run out ofthe magnetic disk.

[0009] In order to reduce the rotational run out of the magnetic disk,it is necessary to reduce the run out attributable to theanti-frictional bearing itself of the spindle motor for driving themagnetic disk. The counter measures having been taken for the problem ofthe rotational run out of the magnetic disk are to improve thesphericity of the rotational bodies of the anti-frictional bearing andto effect the high precision working on the raceway surface of the innerand/or outer races to reduce the working tolerance to the minimum.

[0010] However, an microscopic undulation formed inevitably duringworking or processing on the raceway surface of the inner and/or outerrace will change the relative position of the inner and outer racesduring the operation of the bearing. This changing of the relativeposition will cause the rotational run out. This rotational run out canbe observed as an irregular run out in which the positional relationshipbetween the inner race and the outer race is asynchronous with therotation of the bearing. This run out is known as an asynchronousrotational run out referred to as NRRO (non-repeatable run out).

[0011] When the asynchronous rotational run out is increased beyond theallowable maximum extent, the magnetic head for reading and/or writingdate can not be moved accurately relative to the magnetic disk of hightracking density. This will cause an error in effecting the readingand/or writing datum into disk. In conclusion, the asynchronousrotational run out will fail the reliability of the hard disk device.

[0012] In other words, the asynchronous rotational run out of theanti-frictional bearing to be incorporated into the spindle motor willinterfere the high packaging density and the high speed of the hard diskdevice, i.e. the reduction of the asynchronous rotational run out of theanti-frictional bearing to be incorporated into the spindle motor isextraordinarily important in achieving the high packaging density andthe high speed of the hard disk device.

[0013] The asynchronous rotational run out is influenced by the shape ofthe undulation on the raceway surface of the inner and/or outer racesand the number of rotational bodies interposed therebetween. In order toreduce the asynchronous rotational run out, it is necessary to measurethe out of roundness of the raceway surface accurately, to wake aharmonic analysis on thus obtained value of measurement as describedbelow, and to select the inner and/or outer races which are suitable forthe number of rotating bodies to be interposed therebetween. Theharmonic analysis will now be described as follows.

[0014] Each of the inner and/or outer races has a raceway surfacerepresenting a complex undulation. This undulation can be seized as afunction, the frequency of which is one revolution, i.e. the function isa composite of a plurality of harmonic vibrations.

[0015] In concretely, the shape of raceway surface as shown in FIG.19(a) can be seized as a composite of a harmonic vibration of thefrequency of ⅓ revolution (tertiary vibration) as shown in FIG. 19(b), aharmonic vibration of the frequency of {fraction (1/7)} revolution(seventh vibration) as shown in FIG. 19(c), and a harmonic vibration ofthe frequency of {fraction (1/50)} revolution (fifty vibration) as shownin FIG. 19(d).

[0016] In this connection, the undulation presented on the racewaysurface can be expressed as a following function f(t) including aplurality of frequencies ω, 2ω, 3ω . . .

f(t)=C ₀ +C ₁ cos (ωt+φ ₁)+C ₂ cos (2ωt+φ ₂)+C ₃ cos (3ωt+φ ₃)+ . . .

[0017] In the harmonic analysis, the constant C₀, C₁, C₂, . . . , φ₁,φ₂, . . . are determined.

[0018] In the harmonic analysis effected on the shape of the racewaysurface of the inner and/or outer races, the harmonic vibration of 1/nrevolution forms a shape of an undulation including crests the number ofwhich is n. In this connection, the harmonic vibration of 1/n revolutionis referred to as the undulation including crests the number of which isn. The medial magnitude (C₁, C₂, . . . ) of the displacement amplitudeof the shape varying in a sinusoidal manner is referred to as unilateralamplitude of each number of crests.

[0019] The shape of the raceway surface of each inner race ways, the outof roundness of which are 0.13 μm, 0.096 μm, 0.084 μm, and 0.055 μm isshown in FIGS. 20-23 respectively in the magnification of 100,000. Theresults of the harmonic analysis made on each shapes of the racewaysurface are shown in FIGS. 24-27 respectively.

[0020] The numbers put on the left column of each table are basic numberN, the numbers to be added to the basic number N are put on the upperrow of each table, and the values listed on the table are the values ofunilateral amplitude.

[0021] For example, in the table of FIG. 24, the value put on the fieldof N+0 of the second row (N=7) leans that the component of vibration of{fraction (1/7)} revolution of the shape of the raceway surface as shownin FIG. 20 is 0.002 μm, that is the unilateral amplitude in the casethat the number of crests are seven is also 0.002 μm. The value put onthe field of N+1 of the second row means that the unilateral amplitudein the case that the number of crests are eight is 0.006 μm, and thevalue put on the field of N+2 of the second row means that theunilateral amplitude in the case that the number of crests are eight is0.005 μm. The designation ------ put on the fields of the table meansthat the unilateral amplitude can not be measured, i.e. there aresubstantially no unilateral amplitude.

[0022] The asynchronous rotational run out of the anti-frictionalbearing relates to the shape of the undulation represented on theraceway surfaces of the inner and/or outer race and the number ofrotating bodies as mentioned above. Particularly, it is known that thevalue of unilateral amplitude in the number of crests of aZ and aZ±1 (ais positive integer, and Z is the number of rotating bodies) willinfluence on the rotational run out.

[0023] This is caused by the run out due to the deflection between therotating bodies and the positions of the crests. In this connection,when the anti-frictional bearing, including rotating bodies the numberof which is Z, is intended to be manufactured, the inner or outer racesgreater in its value of unilateral amplitude can not be employed, sincethey will cause the rotational run out of the anti-frictional bearing.

[0024] Concretely, the number of rotating bodies to be utilized for theanti-frictional bearing of the spindle motor of the hard disk device ofthe size equal to or smaller than 3.5 inch is normally from 8 to 12.Explaining on the most general case that the number of rotating bodiesis eight, the values of the unilateral amplitude put on each field ofN+0 (the number of crest is seven), N+1 (the number of crest is eight),and N+2 (the number of crest is nine) of the second row of each of FIGS.24-27 will influence on the rotational run out, so that it is necessaryto reduce these values to 0.002 μm or less than 0.002 μm.

[0025] However, in each table of FIGS. 24-27, the values of theunilateral amplitude on the number of crest from seven to nine does notsatisfy the above mentioned condition, so that the inner racerepresenting the shape of the raceway surface as illustrated in FIGS.20-23 are unsuitable for using in the anti-frictional bearing includingeight rotating bodies.

[0026] As mentioned above, it is necessary in the prior art to makefollowing cumbersome operations to obtain the anti-frictional bearingreduced in its asynchronous rotational run out and thus suitable for thespindle motor of the hard disk device. The above-mentioned operationsare to make a measurement on the out of roundness of the inner and/orouter races, to make the harmonic analysis thereon, and to select theinner and/or outer races based on the relationship between theunilateral amplitude obtained by the harmonic analysis and the nailer ofcrests.

[0027] Accordingly the object of the present invention is to solve theproblems of the prior art. In other words, the object of the presentinvention is to provide an anti-frictional bearing in which theasynchronous rotational run out is reduced substantially, the complexanalyzing operation and the selecting operation to be carried on theinner and/or outer races are unnecessary, and high packaging density andhigh speed of the hard disk device can be assured when it isincorporated into the spindle motor of the hard disk device. Anotherobject of the present invention is to provide a motor including suchanti-frictional bearing.

SUMMARY OF THE INVENTION

[0028] These and other objects are achieved by an anti-frictionalbearing including an inner race way formed on an outer peripheralsurface of an inner race, an outer race way formed on an innerperipheral surface of an outer race, and a plurality of rotating bodiesinterposed between the race ways and retained by retainers in apredetermined distance with each other, wherein an out of roundness of araceway surface of at least one of said inner and outer races is equalto 0.05 μm or less than 0.05 μm.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Further feature of the present invention will become apparent tothose skilled in the art to which the present invention relates fromreading the following specification with reference to the accompanyingdrawings, in which:

[0030]FIG. 1 is a vertical cross sectional view showing theanti-frictional bearing to which the present invention will be applied;

[0031]FIG. 2 is a partially sectional plan view of the anti-frictionalbearing of FIG. 1;

[0032]FIG. 3 is a schematic diagram of the shape of the undulation ofthe inner race way of the anti-frictional bearing in accordance with thepresent invention;

[0033]FIG. 4 is a schematic diagram of the shape of the undulation ofthe inner race way of the other anti-frictional bearing in accordancewith the present invention;

[0034]FIG. 5 is a schematic diagram of the shape of the undulation ofthe inner race way of the further anti-frictional bearing in accordancewith the present invention;

[0035]FIG. 6 is a table representing the result of the harmonic analysiseffected on the inner race way of the anti-frictional bearing as shownin FIG. 3;

[0036]FIG. 7 is a table representing the result of the harmonic analysiseffected on the inner race way of the anti-frictional bearing as shownin FIG. 4;

[0037]FIG. 8 is a table representing the result of the harmonic analysiseffected on the inner race way of the anti-frictional bearing as shownin FIG. 5;

[0038] FIGS. 9-11 are the graphs showing the results of the measurementon the value of the asynchronous rotational run out (NRRO) of thebearing into which the inner race of the present invention having theout of roundness of its inner race way equal to or less than 0.05 μm isincorporated. Also shown in these figures as relatives are the resultsobtained in the measurement on the value of the asynchronous rotationalrun out of the bearing into which the inner race having the out ofroundness of its inner race way from 0.07 μm to 0.08 μm is incorporated,and results of the bearing into which the inner race having the out ofroundness of its inner race way more than 0.10 μm respectively isincorporated.

[0039]FIG. 12 is the graph showing the result obtained from themeasurement test on the value of the rotational torque of the bearing ofthe present invention into which the inner race having the out ofroundness of its inner race way equal to or less than 0.05 μm isincorporated. Also measured in this test as relatives are the resultsobtained in the measurement on the value of the rotational torque of thebearing into which the inner race having the out of roundness of itsinner race way from 0.075 μm to 0.10 μm is incorporated, and that of thebearing into which the inner race having the out of roundness of itsinner race way more than 0.15 μm respectively is incorporated.

[0040]FIG. 13 is a vertical cross sectional view showing an example ofthe motor in accordance with the present invention;

[0041]FIG. 14 is a vertical cross sectional view showing another exampleof the motor in accordance with the present invention;

[0042]FIG. 15 is a vertical cross sectional view showing another exampleof the anti-frictional bearing to which the present invention will beapplied;

[0043]FIG. 16 is a cross sectional view along the line of XVI-XVI inFIG. 15;

[0044]FIG. 17 is a cross sectional view along the line of XVII-XVII inFIG. 15;

[0045]FIG. 18 is a vertical cross sectional view showing the spindlemotor including the anti-frictional bearing as shown in FIG. 15;

[0046]FIG. 19 is schematic diagrams for explaining the principle of theharmonic analysis;

[0047]FIG. 20 is a schematic diagram of the shape of the undulation ofthe inner race way of the anti-frictional bearing in accordance with theprior art;

[0048]FIG. 21 is a schematic diagram of the shape of the undulation ofthe inner race way of the anti-frictional bearing in accordance with theprior art;

[0049]FIG. 22 is a schematic diagram of the shape of the undulation ofthe inner race way of the other anti-frictional bearing in accordancewith the prior art;

[0050]FIG. 23 is a schematic diagram of the shape of the undulation ofthe inner race way of the further anti-frictional bearing in accordancewith the prior art;

[0051]FIG. 24 is a table representing the result of the harmonicanalysis effected on the inner race way of the anti-frictional bearingof prior art as shown in FIG. 20;

[0052]FIG. 25 is a table representing the result of the harmonicanalysis effected on the inner race way of the anti-frictional bearingof prior art as shown in FIG. 21;

[0053]FIG. 26 is a table representing the result of the harmonicanalysis effected on the inner race way of the anti-frictional bearingof prior art as shown in FIG. 22; and

[0054]FIG. 27 is a table representing the result of the harmonicanalysis effected on the inner race way of the anti-frictional bearingof prior art as shown in FIG. 23.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0055] The anti-frictional bearing of the present invention will now bedescribed with reference to the attached drawings.

[0056] The anti-frictional bearing which is the subject of the presentinvention is shown in FIGS. 1 and 2. The balls 3 as rotating bodies ofthe bearing are interposed between the inner race way 1 a provided onthe outer peripheral surface of the inner race 1 and the outer race way2 a provided on the inner peripheral surface of the outer race 2. Theballs 3 are equidistantly retained around the shaft by means ofretainers 4.

[0057] The shape of the undulation of the inner race way 1 a of theanti-frictional bearing is shown in FIGS. 3, 4, and 5 respectively inthe magnification of 100,000. The out of roundness of each shape shownin FIGS. 3, 4, and 5 is 0.048 μm, 0.037 μm, and 0.033 μm respectively.The number of crests and the unilateral magnitude of each inner race wayhaving such shape in its raceway surface derived from the harmonicanalysis are listed in FIGS. 6, 7, and 8 respectively.

[0058] In each inner race way shown in FIGS. 3, 4, and 5, the out ofroundness is equal to or less than 0.05 μm, and the relationship betweenthe number of crest and the unilateral amplitude in the number of crestequal to or above 7(N+0) is equal to or less than 0.001 μm (H means anumber of the rotating bodies included in the bearing) as shown in thetable of 6, 7, and 8.

[0059] In other words, in the case that the out of roundness of theinner race way is equal to or less than 0.05 μm, the unilateralamplitude in the number of crest above 7 are all equal to or less than0.001 μm. In this connection, when the number of rotating bodies areeither of the number from eight to twelve, the unilateral amplitude inthe number of crest from 7 to 13 will be equal to or less than 0.001 μm.This means that the effect on the run out of the bearing will be reducedto a minimum.

[0060] In the case that the out of roundness of the inner race way isequal to or less than 0.05 μm, it is unnecessary to analyze theunilateral amplitude in the number of crest included on the inner raceway to select the inner race to the number of rotating bodies, i.e. suchinner race can be incorporated into the bearing irrespective of thenumber of the rotating bodies. In other words, it is only necessary tomeasure the out of roundness, and the harmonic analyzing operation canalso be eliminated.

[0061] The graphs shown in FIGS. 9-11 are the results of the measurementon the value of the asynchronous rotational run out (NRRO) of thebearing into which the inner race of the present invention having theout of roundness of its inner race way equal to or less than 0.05 μm isincorporated.

[0062] Also shown in these figures as relatives are the results obtainedin the measurement on the value of the asynchronous rotational run outof the bearing into which the inner race having the out of roundness ofits inner race way from 0.07 μm to 0.08 μm is incorporated, and resultsof the bearing into which the inner race having the out of roundness ofits inner race way more than 0.10 μm respectively is incorporated.

[0063] At shown in these figures, it is evident that the one having theout of roundness equal to or less than 0.05 μm is reduced in its NRROcomponents of both outer and inner races.

[0064] Shown in FIG. 12 the result obtained from the measurement test onthe value of the rotational torque of the bearing of the presentinvention into which the inner race having the out of roundness of itsinner race way equal to or less than 0.05 μm is incorporated.

[0065] Also measured in this test as relatives are the results obtainedin the measurement on the value of the rotational torque of the bearinginto which the inner race having the out of roundness of its inner raceway from 0.075 μm to 0.10 μm is incorporated, and that of the bearinginto which the inner race having the out of roundness of its inner raceway more than 0.15 μm respectively is incorporated.

[0066] This measurement test is effected by employing the ball bearinghaving following features: Outer diameter; 15 mm Inner diameter; 5 mmNumber of balls; 8 pcs Rotational speed; 2 rpm Pre-load; 350 gf

[0067] The bearing is of oil lubricating outer race rotating type.

[0068] The reduction of the rotational run out equal to or less than0.05 μm will also reduce the frictional torque of the anti-frictionalbearing.

[0069] Further, it can be ensured that the anti-frictional bearing ofthe present invention is also reduced in its value of andelon, and thatthe required drive power can also be reduced, when using such bearing inthe spindle motor.

[0070] Although in the above-mentioned embodiment, the relationshipbetween the out of roundness and the unilateral amplitude of the innerrace is explained, this relationship can also be obtained in the case ofthe outer race. If it is intended to reduce further the asynchronousrotational run out, it is desirable to make the out of run out of bothof the inner and outer races equal to or less than 0.05 μm.

[0071] Although the ball bearing using balls as rotating bodies isdescribed, the present invention can also be applied equally to theother anti-frictional bearing such as roller bearings.

[0072] The anti-frictional bearing having an arrangement as describedabove is adapted to be used by incorporating into the spindle motor asshown in FIG. 13.

[0073] The spindle motor shown in FIG. 13 is of outer rotor type inwhich a pair of upper and lower ball bearings are interposed between theouter peripheral surface of the spindle shaft 6 secured on the base 5 toextend vertically therefrom and the inner peripheral surface of thevertical bore 8 of the rotor hub 7 so as to support the rotor hub 7rotatably.

[0074] In other words, the motor of the type as shown in FIG. 13, theinner race of each ball bearings 9 is stational, and the outer race isrotatable.

[0075] In FIG. 13, the reference numeral 10 is added to the rotormagnets provided on the inner surface of the downwardly depending flangeof the rotor hub 7, and the reference numeral 11 is added to the statorpositioned opposite to the magnets. The rotor hub 7 is adapted to berotated by providing the electric power to the coils wound around thestator 11. In the case of hard disk drive device, magnetic disk or disks(not shown) are mounted on the outer peripheral surface of the rotor hub7.

[0076] The spindle motor shown in FIG. 14 is an example of the spindlemotor of the inner rotor type in which the spindle shaft 14 is supportedthrough a pair of ball bearings 9 fitted within the sleeve 13 extendingvertically from the base 12. The spindle shaft 14 is formed integrallywith the rotor hub 15.

[0077] In other words, the motor of the type as shown in FIG. 14, theouter race of each ball bearings 9 is stational whereas the inner raceis rotatable.

[0078] In the above-mentioned embodiment, although a ball bearing ofgeneric type in which balls as rotational bodies are interposed betweenthe inner and outer races, the anti-frictional bearing of different typesuch as the compound bearing including two rows of balls as illustratedin FIGS. 15, 16, and 17 can also be employed.

[0079] The anti-frictional bearing shown in FIGS. 15, 16, and 17,spindle shaft 16 is a stepped shaft including an enlarged diameter shaftportion 16 a and a reduced diameter shaft portion 16 b, an outer race isformed by cylindrical sleeve 17, balls 20 as lower rotating bodies areinterposed between the inner race way 18 formed around the outerperipheral surface of the enlarged diameter shaft portion 16 a and thefirst outer race way 19 a formed on the inner peripheral surface of thecylindrical sleeve 17, balls 23 as upper rotating bodies are interposedbetween the inner race way 22 formed on inner race 21 fitted around thereduced diameter shaft portion 16 b and the second outer race way 19 aformed on the inner peripheral surface of the cylindrical sleeve 17, andthe balls 23, 20 of the upper and lower rows are retained equidistantlyaround the shaft with each other by means of retainer 24.

[0080] In the anti-frictional bearing having a structure as mentionedabove, the enlarged diameter shaft portion 16 a included in the spindleshaft will enhance the rigidity of the shaft, so that the durability andanti-vibration property of the shaft is excellent. Further, the innerrace of the lower bearing and outer races of upper and lower bearing areunnecessary so that an advantage that the number of the parts can bereduced will surely be obtained.

[0081] An example of the motor including the anti-frictional bearing ofthe structure as mentioned above is shown in FIG. 18. In such motor,anti-frictional bearing 25 is mounted within the central cylindricalportion 7 a of the rotor hub 7, the rotor hub 7 is journalled rotatablyaround the spindle shaft 16, the shaft 16 and inner race 21 arestational, and the cylindrical sleeve 17 is rotatable.

The Advantages or Effects to be Derived from the Present Invention

[0082] In accordance with the present invention, the unilateralamplitude can be reduced by making the out of roundness of the racewaysurface equal to or less than 0.05 μm. In this connection, thecumbersomeness inherent in the prior art that the number of crest andthe value of unilateral amplitude of inner and outer races are to beanalyzed and selection of the races is to be made to the number ofrotating bodies can be eliminated, the production cost for the bearingcan be reduced, and the asynchronous rotational run out of the bearingcan be improved.

[0083] The reduction of the asynchronous rotational run out will alsoreduce the frictional torque produced within the bearing. This alsoleads to the reduction of the electric power consumed on the spindlemotor of the present invention.

[0084] In the hard disk device including the motor of the presentinvention as a rotational drive means for magnetic disk or disks, highpackaging density of the magnetic disk or disks, or enlarged capacityand fast speed of the hard disk drive device can be realized.

[0085] Making the packaging density of the magnetic disk or diskshigher, the number of magnetic disks to be included within the hard diskdevice can be reduced, the diameter of each magnetic disk can bereduced, the size of the hard disk device itself can be reduced, and theamount of materials used in the magnetic disk or the casing of the harddisk device can also be reduced to save resources.

[0086] In conclusion, reducing of the electric power required in thespindle motor and saving of the resources used for manufacturing thehard disk device will be able to contribute to solving the problem ofthe environmental disruption or pollution.

[0087] While particular embodiments of the present invention have beenillustrated and described, it should be obvious to those skilled in theart that various changes and modifications can be made without departingfrom the spirit and scope of the invention.

What is claimed is:
 1. An anti-frictional bearing including an innerrace way formed on an outer peripheral surface of an inner race, anouter race way formed on an inner peripheral surface of an outer race,and a plurality of rotating bodies interposed between the race ways andretained by retainers in a predetermined distance with each other,wherein an out of roundness of a raceway surface of at least one of saidinner and outer races is equal to or less than 0.05 μm.
 2. Theanti-frictional bearing in accordance with claim 1 wherein; the out ofroundness of the raceway surface of the inner race is equal to or lessthan 0.05 μm.
 3. The anti-frictional bearing in accordance with claim 1wherein; the out of roundness of the raceway surface of the outer raceis equal to or less than 0.05 μm.
 4. The anti-frictional bearing inaccordance with claim 1 wherein; the out of roundness of the racewaysurfaces of the inner race and the outer race are both equal to or lessthan 0.05 μm.
 5. A compound anti-frictional bearing including; a steppedshaft including an enlarged diameter shaft portion on the outerperipheral surface thereof an inner race way is farmed directly and areduced diameter shaft portion around which an inner race is fitted; acylindrical sleeve surrounding the stepped shaft, on the innerperipheral surface of which first outer race way corresponding to theinner race way provided around the outer peripheral surface of theenlarged diameter shaft portion, and second outer race way correspondingto an inner race way provided around the outer peripheral surface of theinner race are formed directly; a first row of rotating bodies retainedby retainers in a predetermined distance with each other between theinner race way provided around the outer peripheral surface of theenlarged diameter shaft portion and the first outer race way of saidcylindrical sleeve; and a second row of rotating bodies retained byretainers in a predetermined distance with each other between the innerrace way provided around the inner race and the second outer race way ofsaid cylindrical sleeve; said compound anti-frictional bearingcharacterized in that: an out of roundness of the raceway surface of atleast one of the inner race way of the enlarged diameter shaft portion,the inner race way of said inner race, the first outer race way of thecylindrical sleeve, or the second outer race way of the cylindricalsleeve is equal to or less than 0.05 μm.
 6. A motor in which a rotor hubis journalled rotatably on the base by means of an anti-frictionalbearing characterized in that a plurality of rotating bodies retained byretainers in the predetermined spacing are interposed between an innerrace way formed on an outer peripheral surface of a inner race and anouter race way formed on an inner peripheral surface of an outer race,wherein a out of roundness of a raceway surface of either of the innerrace way or outer race way is equal to or less than 0.05 μm.
 7. Themotor in accordance with claim 6 wherein; the out of roundness of theraceway surface of the inner race is equal to or less than 0.05 μm. 8.The motor in accordance with claim 6 wherein; the out of roundness ofthe raceway surface of the outer race is equal to or less than 0.05 μm.9. The motor in accordance with claim 6 wherein; the out of roundness ofboth raceway surfaces of the inner and outer races are equal to or lessthan 0.05 μm.